The low impedance (e.g., around several ohms) of high power CO2 slab laser discharges that are energized by RF frequencies in the neighborhood of 100 MHz places electrical constraints on the hermetically sealed RF feed-through connecting the solid state RF power supply to the parallel electrodes inside the laser tube housing. In order to reduce the circulating currents to a minimum and to have a fast rise time (e.g., below 0.1 microsec. at about 100 MHz) in pulsing the discharge, low series inductance is desired for the RF feed-through. The function of the RF feed-through is to deliver fast rise time, high RF power pulses (e.g., having peak powers of a few thousand watts to over 20,000 watts of RF power to a CO2 laser having several hundred watts to 1000 W of output IR average output power, respectfully) into a laser discharge within a hermetically sealed metal “tube” chamber without emitting stray RF radiation into the atmosphere. This tube chamber contains the appropriate gas mixture of CO2:N2:He, etc., at below atmospheric pressure (i.e., typically between 60-150 Torr), the mirrors forming the laser's optical resonator, and the two long parallel facing metal electrodes between which the laser's discharge is generated. Depending upon the laser power desired, the gap between the two parallel facing electrodes and the width and the length dimensions of the electrodes varies with the desired output power of the laser, gas pressure, the RF frequency, the gas temperature, etc. For a 500 W CO2 slab laser, the electrode length is in the neighborhood of 800 mm. and the width is typically slightly larger than one tenth ( 1/10) of the length. The laser tube has a rectangular or cylindrical configuration, typically fabricated from aluminum. For a 500 W laser, the open ends of the laser tube are typically of the order of 150 mm. The distance between the mirrors of the resonator is slightly longer than the length of the electrodes. For an electrode length of approximately 800 mm, the distance between the mirrors is approximately 870 mm.
From uniform discharge considerations, it is desirable to have the electrical RF contact made by the hermetically sealed feed-through to the electrodes occur at the center of the length of the electrode. The small aspect ratio of the contact opening to the length of the laser tube housing makes this contact mechanically difficult to accomplish. Consequently, as disclosed in commonly-assigned U.S. Pat. No. 5,155,739, RF contact has been made to one end of the electrode pair by placing the feed-through at one of the end flanges of the laser housing tube.